This invention relates to a bearing material. More particularly, the invention relates to a bearing material which is most suitable for reciprocating motion mechanisms receiving large and fluctuating loads.
Unlike the bearings of common machine tools which bear the rotations in one direction, the bearings used for reciprocating motion mechanisms such as shock absorbers of automobiles are liable to receive unsymmetrical contacts, and they are subjected to uneven wear by reciprocating sliding motions. Therefore, the bearing material for such reciprocating motion mechanisms must have excellent load resistance and wear resistance as compared with those for the conventional machine tools. Further, in the case of the double-layered bearing material employed in the present invention, adherence between the sliding surface material and the back metal is also required.
As the bearing material for reciprocating sliding mechanisms such as the shock aborbers of automobiles, a copper-lead alloy or the like has heretofore been employed. With the recent improvement of high-powered engines and high-speed sliding mechanisms, however, a bearing material which bears up against large loads and high-speed sliding is demanded. Further, when unsymmetrical contact is caused to occur in the sliding portion in oil, the oil film is often broken and boundary lubrication is brought about, thus the frictional resistance increases considerably and smooth sliding cannot be expected. In addition, the wear of the material becomes a problem. By the way, the frictional resistance of course becomes large when bearings are used in a dried condition.
As for the bearing material which is not especially restricted to the use for reciprocating sliding members and contains plastics generally having low dry frictional resistance, as disclosed in U.S. Pat. Nos. 2,995,462 and 3,416,941, it is well known that the bearing material is made by a method in which a porous sintered layer of iron or copper powder on a back metal is coated by polytetrafluoroethylene resin, hereinafter referred to as "PTFE," or by a mixture of PTFE and fillers such as lead, lead oxide, thallium, cadmium, cadmium oxide, indium, molybdenum disulfide, aluminum oxide, iron oxide and zinc oxide. These bearing materials are often used for one directional sliding in the rotation of ordinary machine tools. However, under the severe conditions of reciprocating sliding motion wherein large and fluctuating loads are applied, the wear of the bearing surface often becomes large, or the coated layer is scraped off. Therefore, the above-mentioned bearing material cannot be used for such severe conditions.